Measuring light intensity
How bright is bright? Measure it in lux.
How bright?
Light intensity is how bright light is. Our eyes adjust, so we are not good at judging brightness. A light meter measures it accurately.
Sunlight on a clear summer day can be over 100,000 lux, while a well-lit classroom is about 500 lux.
Lux
Light intensity is measured in lux. A dim room might be about 50 lux; a bright classroom about 500 lux. Full sunshine can be over 100,000 lux.
The word lux comes from the Latin word for light.
Distance and brightness
As light spreads out from a source, it gets weaker. The further you are from a lamp, the lower the light meter reading. This is why we read near a lamp, not across the room.
Doubling your distance from a lamp makes the light about four times weaker, because it spreads over four times the area.
Light for health
Reading and writing need enough light to avoid eye strain. Schools and offices use light meters to check rooms are bright enough.
Schools try to use daylight from windows during the day – it is free, and it is good for learners’ eyes and mood.
What I learnt
- I know that light intensity is measured in lux with a light meter.
- I know that light gets weaker further from the source.